With dietary diversification and increasing consciousness towards safety, security and health in recent years, many acidulous foods have been provided in particular.
Much importance has been placed on acids such as acetic acid and lactic acid not only because acids improve the shelf life, but also as a health-oriented food. However, if a sourness, a bitter taste, an astringent taste, a harsh taste or the like is too strong, it becomes difficult to eat the food. For example, there arises the problem that when a fermented milk drink is stored over a long period of time, fermentation proceeds too much and the sourness becomes too strong to appreciate. In addition, from a viewpoint of dieting, artificial sweeteners with fewer calories tend to be frequently used for a sweet taste. However, artificial sweeteners have a distinctively bad aftertaste and reduce palatability, which is problematic.
Although the taste of peptides has long been examined, many of the investigations are related to the bitter taste of peptides or related to a method for improving the bitter taste (Non-patent document 1 and Patent Document 1). On the other hand, as peptides leading to improvement of the quality and value of a food or a drink, peptides such as 4-residue peptide represented by Tyr-Glu-Glu-Glu or Tyr-Glu-Glu-Asp found during hydrolysis of an extraction residue of dried and fermented fish (Patent Document 2), the peptides with more than 11 residues such as Ala-Pro-Pro-Pro-Pro-Ala-Glu-Val-His-Glu-Val-Val found in a water extract of pork (Patent Document 3), the peptides having the sequence Trp-Val, Trp-Tyr, Tyr-Trp, Trp-Ile, Trp-Leu or Glu-Ile-Leu, respectively, which were found in an enzymatic decomposition product of milk protein such as α-lactalbumin, and have a taste-improving effect such as enhancing a richness, a savory taste (umami) and a sense of volume (Patent Document 4), and the peptides with a molecular weight of 200 to 20,000 obtained by hydrolyzing albumen (Patent Document 5) are known.
However, the taste-improving agents described in the above related art merely have an effect of imparting or enhancing a richness and a savory taste (umami), or their other taste-improving effects are not always sufficient. Especially, a sourness-masking effect and an aftertaste-improving effect of an artificial sweetener are insufficient.
In addition, it is also reported that Ile-Pro-Pro or Val-Pro-Pro which is a tripeptide having an angiotensin-converting enzyme inhibitory activity is used as an anti-stress agent (see Patent Document 6). However, these peptides are different from the peptide of the present invention and a taste-improving effect is not reported.